1. Field of the Invention
This invention relates to a testing method for evaluating abrasion properties of a friction member in a member such as a brake or a clutch for use in automobiles, industrial vehicles and industrial machines and a mating member with which the friction member is put into sliding contact.
To be more specific, this invention relates to a method of evaluating the abrasion of a disk rotor (hereinafter simply referred to as a disk) resulting from the contact between a pad and the disk of a disk brake while a vehicle equipped with such a disk brake is running and not braked.
2. State of the Prior Art
Various means are known for evaluating the abrasion properties of a friction member such as a pad and a mating member such as a disk. In any of these means, the test is conducted by bringing either a test piece of the mating member and the friction member or an actual mating member and friction member into frictional contact with each other.
A testing machine under JIS D4411 and SAE J661a represents a typical example adopting the former method. As a typical example adopting the latter method, as shown in FIGS. 4 and 5, there is known an inertia type dynamometer having a rotary shaft 1 to which a disk 2 is mounted. Friction members 3 are provided at both sides of the disk 2 to clamp and brake the disk.
The aforementioned testing machines are suitable for the evaluation of the abrasion of a friction member but not for the evaluation of the abrasion of a disk.
The machine under JIS D4411 is adapted to test a disk-shaped mating member. But it is not a disk which is actually used in a disk brake, and it must have a shape peculiar to this machine. Due to this difference in shade between the actually used disk and the disk tested in this machine, the evaluation results will not necessarily reflect the abrasion properties of the actual disk. The machine under SAE J661a uses a drum type mating member, which does not suit the object. Further, no consideration is taken of measurements on the order of microns or measurements of continuous abrasion marks. Thus, no detailed data about the disk are obtainable. Also, the surface pressure applied during the test is 10 kg or more. Testing is impossible at lower pressures.
In the methods in which a disk and a friction member are both tested in the form of test pieces, it is troublesome to cut off such test pieces and fit them on the testing machine, which is one of the factors raising costs. Further, since the test is conducted on a smaller scale, there might be errors in the evaluation results due to the difference in conditions between the actual machine and the testing machine. Thus, such errors have to be corrected. In order to verify the corrected values, a correlation check will be necessary.
On the other hand, the inertia type dynamometer can evaluate the actual abrasion between a disk and a friction member because abrasion is tested between actual examples of both members. But this type of tester is extremely expensive. Further, due to irregular shapes of the friction members, it is necessary for high accuracy to correct the evaluation results of the abrasion of the disk.
The abrasion of the disk due to frictional contact between the disk and the pads while not braked is becoming a big problem, especially in the United States, where automobiles are driven at higher speed and the intervals between brake applications are longer. Namely, due to partial frictional contact between pads and a disk, the disk tends to be abraded locally and its thickness tends to be uneven. When brakes are applied thereafter, the pads which sandwich the disk from both sides will be repeatedly pushed back and forth by the rotating disk due to changes in the thickness thereof, thereby giving the driver extreme uneasiness.
To prevent this, it is essential to find better materials for the disk and the pads. But there has been no suitable evaluation means for determining the quality of the materials. For this purpose, it may be possible to test the abrasion of a disk actually mounted on a car or such tests may be conducted by use of a dynamometer as described above. But the on-the-car test requires that the car be driven 5,000 km or more, and the repeatability is bad. The dynamometer test requires more than 100 hours of testing time, and the repeatability is bad, too.
Further, when evaluating only abrasion, the on-the-car test and the test with a dynamometer pose the following problems.
Pads are usually disposed between the disk and the piston. While braking, they are pressed against the disk. When the brakes are released, the piston retreats slightly. The pads are thus freed between the piston and the disk. But due to vibrations while the car is moving, they will contact the disk. Further, it is impossible to mount the disk perfectly parallel to a pad or the piston. Rather, it tends to be inclined at the rate of about 0.05-0.10 mm/m. Thus, a portion of the disk near each pad will hit the pad once per rotation. The degree of such contact between the disk and the pads varies greatly among different tests depending upon the position of the pads while they are free, dimensions of the disk and the piston, a change in inclination during testing, and the degree of abrasion of the pads. Thus, these tests have a fatal problem in that the characteristics of the pads and the disk are mixed and lost in these many variable factors.
It is an object of this invention to provide an abrasion testing method which is free of these problems.